2.
Chalk used in school classrooms comes
in slender sticks approximately .35 of an
inch (nine millimeters) in diameter and
3.15 inches (80 millimeters) long.
Lessons are often presented to entire
classes on chalk-boards (or blackboards,
as they were originally called) using
sticks of chalk because this method has
proven cheap and easy.
3.
As found in nature, chalk has been used for
drawing since prehistoric times, when,
according to archaeologists, it helped to
create some of the earliest cave drawings.
Later, artists of different countries and
styles used chalk mainly for sketches, and
some such drawings, protected with shellac
or a similar substance, have survived. Chalk
was first formed into sticks for the
convenience of artists.
4.
The method was to grind natural chalk to a
fine powder, then add water, clay as
a binder, and various dry colors. The
resultant putty was then rolled into cylinders
and dried. Although impurities produce
natural chalk in many colors, when artists
made their own chalk they usually
added pigments to render these colors
more vivid. Carbon, for example, was used
to enhance black, and ferric oxide (Fe2O3)
created a more vivid red.
5.
Almost all chalk produced today is dustless.
Earlier, softer chalk tended to produce a
cloud of dust that some feared might
contribute to respiratory problems. Dustless
chalk still produces dust; it's just that the dust
settles faster. Manufacturers accomplish this
by baking their chalk longer to harden it more.
Another method, used by a French company,
is to dip eighty percent of each dustless chalk
stick in shellac to prevent the chalk
from rubbing off onto the hands.
6.
Chalk did not become standard in schoolrooms until
the nineteenth century, when class sizes began to
increase and teachers needed a convenient way of
conveying information to many students at one time.
Not only did instructors use large blackboards, but
students also worked with individual chalkboards,
complete with chalk sticks and a sponge or cloth to
use as an eraser. These small chalkboards were used
for practice, especially among the younger students.
Pens dipped in ink wells were the preferred tool for
writing final copy, but these were reserved for older
students who could be trusted not to make a mess:
paper—made solely from rags at this time—was
expensive.
7.
An important change in the nature of classroom
chalk paralleled a change in chalk-boards.
Blackboards used to be black, because they
were made from true slate. While some experts
advocated a change to yellow chalkboards and
dark blue or purple chalk to simulate writing on
paper, when manufacturers began to fashion
chalkboards from synthetic materials during
the twentieth century, they chose the color
green, arguing that it was easier on the eyes.
Yellow became the preferred color for chalk.
8. To make white classroom chalk, the
manufacturer adds water to form a
thick slurry with the consistency of clay. The
slurry is then placed into and extruded from
a die—an orifice of the desired long, thin
shape. Cut into lengths of approximately
24.43 inches (62 centimeters), the sticks are
next placed on a sheet that contains places
for five such sticks. The sheet is then placed
in an oven, where the chalk cures for four
days at 188 degrees Fahrenheit (85 degrees
Celsius). After it has cured, the sticks are
cut into 80 millimeters lengths.
9.
Many people consider using chalk and
chalk-boards to present
material outdated. Some experts claim
that teachers have stubbornly resisted
new technologies that could improve
teaching—and eliminate the chalkboard
entirely. A study which recently
investigated whether teaching with
overhead projectors was more effective
than using chalkboards concluded that
chalkboards were more interactive,
progressive, and fruitful.
10.
A development much in the
educational news lately is the
electronic chalkboard. In place of a
regular chalkboard, a teacher uses a
large TV screen, inputting materials
from a computer terminal. In a more
advanced scenario, each student uses
a terminal, to which the teacher sends
information from a master computer.
11. Experts claim that such set-ups are more
visually exciting to students, more versatile than
the old-fashioned chalkboards, cleaner than
dusty chalk, easier for the teacher to use, and
better able to present more complex material
through the use of graphics and animation. Many
studies on the feasibility of electronic
chalkboards have been made, however, and most
seem to favor keeping the traditional chalkboard,
at least for now. Electronic chalkboards that are
sophisticated and easily readable lie beyond the
budget constraints and technological capabilities
of most schools.
